# Human Skin as an Ex Vivo Model for Maintaining Mycobacterium leprae and Leprosy Studies

## TL;DR

Human skin is used as a model to study Mycobacterium leprae, the bacteria causing leprosy, offering a new alternative to traditional animal models.

## Contribution

The study presents a standardized ex vivo human skin model for maintaining M. leprae and studying its interactions with the host.

## Key findings

- M. leprae was successfully maintained in human skin explants for 60 days.
- Recovered bacilli showed viability and infectivity in mice, with the highest positivity at day 28.
- Cytokine gene expression patterns varied depending on whether bacilli were alive or dead.

## Abstract

The in vitro cultivation of M. leprae has not been possible since it was described as causing leprosy, and the limitation of animal models for clinical aspects makes studies on leprosy and bacteria–human host interaction a challenge. Our aim was to standardize the ex vivo skin model (hOSEC) to maintenance and study of M. leprae as an alternative animal model. Bacillary suspensions were inoculated into human skin explants and sustained in DMEM medium for 60 days. Explants were evaluated by RT-PCR-16SrRNA and cytokine gene expression. The viability and infectivity of bacilli recovered from explants (D28 and D60) were evaluated using the Shepard’s model. All explants were RT-PCR-16SrRNA positive. The viability and infectivity of recovered bacilli from explants, analyzed after 5 months of inoculation in mice, showed an average positivity of 31%, with the highest positivity in the D28 groups (80%). Furthermore, our work showed different patterns in cytokine gene expression (TGF-β, IL-10, IL-8, and TNF-α) in the presence of alive or dead bacilli. Although changes can be made to improve future experiments, our results have demonstrated that it is possible to use the hOSEC to maintain M. leprae for 60 days, interacting with the host system, an important step in the development of experimental models for studies on the biology of the bacillus, its interactions, and drug susceptibility.